Lift control systems



Jan. 6, 1959 w. J. BAILEY LIFT CONTROL SYSTEMS Filed Jan. 2, 1958 (IL/14(M63 mg 81/ DSR/ 3 Sheets-Sheet 1 United States PatentO Claims priority,application Great Britain January 14, 1957 16 Claims. (Cl. 187-29)assignor to J. & E. a company of Great This invention relates to liftcontrol systems and is concerned with lift control systems of the kindin which a plurahty of cars is arranged for serving a number of floors,the system being capable of operating the cars in any one of a pluralityof diiierent modes, the different -modes being appropriate to differenttraffic conditions.

According to a first aspect of the present invention there is provided alift control system for a plurality of cars arranged to serve a numberof floors, the system comprising means for operating the cars in any oneof a plurality of different modes, said modes includinga first mode ofoperation that is suitable for heavy trafiic in one direction and asecond mode of operation that is suitable for normal trafiic conditions,means associated with each car for determining whether the car isloaded, and selection means for causing the cars to be operated in thefirst mode when a predetermined time relationship exists between theperiods during which loaded cars are travelling in said one directionand for causing the cars to be operated in said second mode when noother mode is selected.

According to another aspect of the present invention there is provided alift control system for a plurality of cars arranged to serve a numberof floors, the system comprising means for operating the cars in any oneof a plurality of different modes, said modes including a first mode ofoperation that is suitable for heavy up traffic, a second mode ofoperation that is suitable for heavy down traffic and a thirdmode ofoperation that is suitable when there is heavy traffic in neitherdirection, means for each car for determining whether the car is loaded,first means for each car for registering the loaded condition of the carwhen the latter is travelling upwardly, second means for each car forregistering the loaded condition of the car when the latter istravelling downwardly, and selection means for causing the cars to beoperated in the first mode when a first predetermined number of thefirst registering means have been operated for periods between adjacentones of which there is not more than a first predetermined time intervalduring which none of the first registering means is operated, forcausing the cars to be operated in the second mode when a secondpredetermined number of the second registering means have been operatedfor periods between adjacent ones of which there is not more than asecond predetermined time interval during which none of the secondregistering means is operated, and for causing the cars to operate inthe third mode when no other mode is selected.

According to a further aspect of the present invention there is provideda lift control system of the kind referred to, wherein mechanism isprovided for selecting the mode in which the system will operate, theselection being made in accordance with the relative amounts of up anddown trafiic as assessed by the loading of the cars and the directionsin which the cars are travelling.

For a better understanding of the invention and to show how the same maybe carried into effect reference will be made to the accompanyingdrawings in which Figure 1 is a circuit diagram of mechanism forselecting the mode of operation of a lift system and Figures 2 and 3 arekey sheets for Figure 1 showing the relay coils and their associatedcontacts in spindle form.

To facilitate an understanding of the lift system the followingapparatus is listed:

BLba1anced peak selector relay coil;

DA, DB and DC--down coils of the cars A, B and C respectively;

DLA, DLB and DLC--down load relay coils for the cars A, B and Crespectively;

DPTdown peak hold relay coil;

DSR-down peak selector relay coil;

LSRA, LSRB, LSRC--load switch relay coils for the cars A, B and Crespectively;

UA, UB and UC-up coils for the cars A, B and C;

ULA, ULB and ULC-up load relay coils for the cars A, B and Crespectively;

UPTup peak hold relay coil;

USR-up peak selector relay coil.

The lift system is a modified form of that disclosed in co-pendingPatent application No. 641,184 in which a plurality of cars serve anumber of floors or landings. The cars are arranged upon completion of atrip ordinarily to return to a particular floor which is termed thedespatching floor. If, however, the system is arranged to operate with afree car (as described in said co-pending application), as calls arecleared the last car to be working remains at the floor to which it islast called and constitutes a free car. Movement of each car isinitiated eitherby a car call which is made by a person in the car andwho desires to travel to a certain floor, or by a landing call that isinitiated by a passenger waiting at one floor and who desires to travelto another floor. Landing calls are supervised by a despatch signalinitiating system to determine whether a landing call can convenientlybe attended to by a car already on a trip or whether a further car thatis waiting at the despatching floor should be despatched to attend tothe landing call. The despatch signal initiating system selects theorder for despatch of the cars and is arranged to delay the despatchsignal until the expiry of a predetermined despatch interval, thedespatch interval for each car being initiated when the despatch signalis given to the previously selected car. Thus the despatch interval isan interval during which a car cannot be despatched to respond to alanding call. The system is arranged for selecting either the upperterminal floor or the lower terminal floor (ignoring any basement) asthe despatching floor. When the lower terminal floor is selected as thedespatching floor the system is said to be on up despatch and when theupper terminal floor is selected as the despatching floor the system issaid to be on down despatch. Means are provided for varying the despatchinterval, either to be a long interval or to be a short interval. In theaforementioned co-pending application a manual trafiic selection switchis provided. This switch has three operative positions. The switch isadjusted to its first operative position to deal with heavy downtraflic, to its second operative position to deal with normal trafiicconditions and to its third operative position to deal with heavy uptraflic. The first position is known as down peak and in this positionthe system is caused to operate with downward despatch and with theshorter despatch interval. In the third position which is known as uppeak the system is caused to operate with upward despatch and theshorter despatch interval. In the second operative position which is thenormal position for balanced traflic the system operates on upwarddespatch with a variable despatch interval, the despatch interval beingarranged to be long or short according to the positions of the cars inthe l atentetl Jan. 6, 1959 .ing calls.

hatchways, the directions of travel of the cars and whether the cars areunder despatch. (A car is under despatch when it has received itsdespatch signal but has not yet departed from the despatching floor).

The circuitry shown in the drawing of the present cas replaces themanual means described in said co-pending application for selecting themode of operation of the lift system, by means for automaticallyselecting the mode of operation in accordance with the trafficconditions of the system. The present automatic system is arranged forselecting one of four modes'of operation, viz. normal, up peak, downpeak. and balanced peak. The normal mode of operation is identical withthe normal mode of operation of the system of said co-pendingapplication. When on up peak the lift system operates with upwarddespatch and with the shorter despatch interval, some of the cars beingarranged for by-passing certain down land- When on down peak the systemoperates with downward despatch and with the shorter despatch interval,some of the cars being arranged for by-passing certain up landing calls.When on balanced peak, the lift system operates on upward despatch withthe shorter despatch interval but there is no such by-passing of callsas with up peak and down peak. Selection of the mode of operation of thesystem is effected by three coils, viz. an up peak selector relay coilUSR, a down peak selector relay coil DSR and a balanced peak selectorrelay coil BL. When the coil USR is energised the lift system operateson up peak. When the coil DSR is energised the system operates on downpeak, when the coil BL is energised the system operates on balanced peakand when none of these three coils is energized the system operates onthe normal mode. In Figure 1 relay coils have been indicated by a circlewith the coil reference in the circle. indicated by the conventionalsymbol.

Referring now to the circuit diagram in greater detail, a movable arm MAof a manual selector switch MSS is capable of assuming five operativepositions and in these positions respectively connects contacts A to Eto a positive supply line ML, there being a negative return line EL. Thecontact A is connected to a line L1 and when the manual selector switchis positioned to connect the line ML to the line L1 the lift systemoperates with automatic selection. anism will be described for use witha lift system having three cars, A, B and C (not shown) but it is to beunderstood that the mechanism can with slight modification be applied tosystem having any number of cars greater than one. Each car has thereina load switch (not shown) that is closed when the car is loaded to apredetermined extent. energising an associated load switch relay coil(not shown) and each such coil when energized closes two associatedpairs of contacts. The contacts for the car A are LSRAl and LSRAZ, forcar B LSRBI and LSRB2 and for car C LSRCl and LSRC2. Two main controlcoils (not shown) are associated with the driving motor (not shown) ofeach car of the lift system. One of these two coils is an up coil whichis energized to cause the motor to drive its car in the upward directionand the other coil is a down coil that is energised to cause the motorto drive its car downwardly. The up coils of the cars A, B and C eachcontrol two pairs of contacts and these are respectively UAE and UA2,UB1 and UB2, and UCl and UC2. Similarly, the down coils (not shown) ofthe cars A, B and C respectively control contacts DAl and DA2, DB1 andDB2, and DCl and DC2.

One, contact of the pair of contacts LSRAl is connected to the line L1and the other contact is connected to a. junction point J'Pl. Onecontact of the pair LSRBl is connected. to the line L1 and the other isconnected to a junction point JP2. One contact of the pair LSRCI isconnected to the line L1 and the other contact is connected to ajunction point JP3. The junction points In Figures 2 and 3 relay coilshave been The automatic selection mech- Each load switch is arrangedwhen closed for JP1, JP2 and J P3 are respectively connected throughcontacts UA1, UB1 and UCl to a terminal 5 joined to the control grid ofa valve V1 of a timer TX. The junction points JP1, JP2 and JP3 are alsorespectively connected through contacts DAI, DB1 and DC to a terminal 5joined to the control grid of a valve V2 of a timer TY. The cathode ofthe valves V1 and V2 are each connected through an associated terminal 3to the negative line EL. The anode of the valve V1 is connected througha terminal 4 and an up peak hold relay coil UPT to the line L1. Theanode of the valve V2 is connected through an associated terminal 4 anda down peak hold relay coil DPT to the line L1.

The cathodes of the valves V1 and V2 are heated by the secondary windingof a transformer T the primary of which is connected across an A. C.supply.

Assuming that the line L1 is connected by the switch MSS to the line MLso that a positive potential is applied to the line Ll, the valves V1and V2 immediately conduct whenever the positive potential of line L1 isapplied to their control grids. Following interruption of the circuitapplying positive potential to the control grid of either of the valves,the associated valve ceases conducting approximately two minutes aftersuch interruption.

One contact of the pair of contacts LSRA2 is connected to the line L1and the other contact of this pair is connected to a junction point 1P4.The contacts LSRBZ are connected between the line L1 and a junctionpoint J P5 and the contacts LSRCZ are connected between the line L1 anda junction point 1P6. The point JP4 is connected through the contactsUA2 and an up load relay coil ULA for the car A to the line EL. PointJPS is connected through the contacts UB2 and an up load relay coil ULBfor the car B to the line EL and the point 1P6 is connected through thecontacts UC2 and an up load relay coil ULC for the car C to the line EL.The point J P4 is also connected through the contacts DA2 and a download relay coil DLA for the car A to the line EL, the point 1P5 isconnected through the contacts DB2 and a down load relay coil DLB forthe car B to the line EL, and the point JP6 is connected through thecontacts DCZ and a down load relay coil DLC for the car C to the lineEL. 7 The coil UPT controls contacts UPTI, the coil DPT controlscontacts DPTl, the coil ULA controls contacts ULAl to ULA4, the coil DLAcontrols contacts DLAl to DLA4, the coil ULB controls contacts ULB1 toULBd, the coil DLB controls contacts DLBl to DLB4, the coil ULC controlscontacts ULCl to ULC4 and the coil DLC controls contacts DLCl to DLC4.One contact of the pair of contacts UPTl is connected to the line L1 andthe other contact is connected to a junction point .lP7. One contact ofthe pair DPTl is connected to the line L1 and. the other is connected toa junction point TF3. The positive sides of the coils ULA, ULB, ULC arerespectively connected through contacts ULAl, ULBI and ULCl to thejunction point 3P7 and the positive sides of the coils DLA, DLB and DLCare respectively connected via the contacts DLA DLBl and DLCl to thejunction point JP8.

The coil USR controls contacts USRl, USR2 and others (not shown), thecoil DSR controls contacts DSRl, DSR2 and others (not shown) and thecoil BL controls contacts BLl to BL4 and others (not shown).

The contacts ULA2, ULB2 and ULC2 are connected together in seriesbetween the line L1 and a junction point 3P9, this point being connectedthrough the contacts BLl and DSRI and the coil USR to the line EL. Thecontacts DLA2, DLB2 and DLC2 are connected together in series betweenthe line L1 and a junction point IP10 which is connected to the line ELthrough the contacts BL2 and USRl and the coil DSR.

One side of the coil BL is connected to the negative line EL and theother side of the coil is connected to a junction point JP11. The pointJP11 is connected to a line L2 through parallel connected contacts BL3and DSRZ. A

line L3 is connected to the point JP11 through parallel connectedcontacts USR2 and BL4. The line L2 is connected to the line L1 throughthree parallel paths, the first of which consists of series-connectedcontacts ULA3 and ULB3, the second consisting of series-connectedcontacts ULA4 and ULC3 and the third consisting of series-connectedcontacts ULB4 and ULC4. The line L3 is connected to the line L1 throughthree parallel paths, the first of which consists of series-connectedcontacts DLA3 and DLB3, the second consisting of seriesconnectedcontacts DLA4 and DLC3 and the third consisting of series-connectedcontacts DLB4 and DLC4.

The contacts C and D of the manual switch MSS are respectively connectedto the junction points P9 and IP10. The contact E is connected to anearth return line through a relay coil which is energised when it isdesired to put the lift system of said copending ap plication on nightservice.

A movable arm MAI of a clock selector switch CSS is connected to theline L1. The arm MAl is clock driven to rotate once every twenty-fourhours. The arm MAI successively encounters segments 9, 12, 15, 18. The.arm is in contact with each of these segments for a predeterminedperiod, the segment 9 at a period around 9 a. m., the segment 12 at aperiod about noon, the segment at a period about 3 p. m. and the segment13 at a period about 6 p. m. The segments 9 and 15 are connected to thejunction point JP9 and the segments 12 and 18 to the junction pointIP10.

With the arm MA of the switch M58 in the position where the armtouchesthe contact A, the mechanism is set for automatic operation. Let it beassumed that all the cars are standing idle at the lower terminal floor.The mode of operation set by the mechanism is normalf since the coilsUSR, DSR and BL are all deenergised. When calls for service areregistered from the landings or by passengers in the cars, the carsanswer these calls in the manner described in said co-pendingapplication. So long as the loads in the cars do not exceed the pre-setvalue at which the load switches close, the lift system remains in thenormal mode of opera tion (ignoring for the moment the function of theclock selector switch CSS).

If the load in, say, car A exceeds the pre-set value at some timeduring, say, the upward travel of this car, the load switch for car Awill close and hence contacts LSRAl and LSRA2 close. Contacts UAl andUA2 are already closed as the car is travelling upwardly. Hence thevalve V1 conducts and the coil UPT is energised and the contacts UPTlare closed. Closure of the contacts LSRA2 and UA2 causes energisation ofthe up load coil ULA whereby contacts ULA]; to ULA4 close. ContactsUPT]. and ULAl form a holding circuit for the coil ULA and this coil ismaintained energised until the contacts UPTll open, i. e. when the coilUPT becomes de-energised. The coil UPT becomes de-energisedapproximately two minutes after removal'of the positive potential fromthe control grid of the valve V1. Thus provided car A is the only oneupon which the load switch has operated, the coil ULA becomesde-energised approximately two minutes after car A reverses or after theload switch opens whichever is the earlier. Similarly, if the load incar A exceeds the preset value at some time during downward travel ofthe car A, the coil DLA is energised and holds for the pre-set timeafter opening of the contacts LSRAl or DAll. For cars B and C, the coilsULB, DLB, ULC and DLC operate similarly to the coils ULA and DLA.

When car A is travelling upwardly in the loaded condition the contactsLSRAll andUAl are closed as are the contacts LSRAZ and UA2 so that thecoils UPT and ULA are energised. If car B is in a condition where it istravelling upwardly with its load switch closed at a time less than twominutes after reversal of the car A or opening of the load switch in carA, the coil ULB will of course have become energised and in addition thecoil ULA will be maintained energised, since the'coil UPT remainsenergised following closure of the contacts LSRBl and UB1, whereby theholding circuit for the coil ULA is maintained closed. If now car Ctravels upwardly with its load switch closed at a time less than twominutes after the last of cars A and B to reverse has done so or afterthe last of cars A and B to be unloaded has become so or after one ofthem has reversed and the other has become unloaded, the coil ULC willbe energised and the coils ULA and ULB will be maintained energised.When all three of coils ULA, ULB and ULC are energised, the contactsULAZ, ULB2 and ULCZ in series with the up peak selector relay USR areclosed and as the contacts BL and DSRl are at this time closed the coilUSR is energised and the lift system operates on up peak. in practice,of course, de-energisation of the coil UPT occurs as a result of openingof the load switches rather than reversal of the cars since the carsordinarily become unloaded before they reverse.

The coils DLA, DLB and DLC control the down peak selector relay coil DSRin a similar way to the control exercised over the coil USR by the coilsULA, ULB 'and ULC. Thus it can be said that when cars A, B and C haveall become loaded beyond a pre-set value for the same direction oftravel and the interval between the periods of. such loadings has notexceeded the time (approximately two minutes) set by timer TX or TY thecoil USR is energised in the case of upward travel and the coil DSR isenergised in the case of downward travel. The coil USR remains energisedfor the pre-set time, set by timer TX, after all of the upwardtravelling cars A, B and C have reduced their loadsbelow the pre-setvalue. Similarly the coil DSR remains energised for the time set by thetimer TY after all the downward travelling cars A, B and C have reducedtheir loads below the pre-set value.

With the circuit as shown, the relay coils USR and DSR cannot responduntil all three cars have been loaded beyond the pre-set value, but itis to be understood that these relay coils can be arranged so that theyrespond to loading of any number of cars of the group as desired to suitthe requirements of a particular installation.

The coils USR and DSR when energised respectively select up peak anddown peak modes of operation of the lift system. It will be realisedthat once the selection has been made it is held for a pre-set time(about two minutes) after the subsidence of the peak and this time lagcan, of course, be adjusted as desired by alteration of the timecircuits of the valves V1 and V2. The time lag prevents selectionchanges taking place at two frequent intervals and thus short gapsbetween peak traffic conditions for the same direction do not causediscontinuance of peak selection. t

Assume now thatthe condition of traffic is for up peak so that the relaycoil USR is energised. If any two cars become loaded beyond the pre-setvalue in the downward direction, one of the three parallel paths betweenthe lines L3 and L1 will be completed and as the contacts USR areclosed, the coil BL will become energised. Energisation of the coil BLcloses the contacts BL4, and opens the contacts BLI. Opening of thecontacts BLT causes the coil USR to be de-energised and closure of thecontacts 3L4 maintains the coil BL in the energised condition in spiteof the opening of the contacts USR2. The lift system therefore assumesits balanced peak mode of operation. Similarly, when down peak tralticconditions exist so that the coil DSR is energised, loading of any twocars beyond the pre-set value whilst they are travelling upwardly causesthe coil BL to become energised whereby the contacts BL2 open and BL3close, the coil DSR becoming de-energised and the coil 7 BL beingmaintained energised by closure of the contacts BL3.

If first the up peak or the down peak trafiic condition subsides, themode of operation reverts to normal be cause all of the relay coils USR,DSR and BL are deenergised. If the balanced peak traffic condition firstsubsides, the mode of operation reverts to the prevailing up or downpeak because the coil BL becomes deenergised.

The following table shows typical trafiic conditions and the point atwhich automatic selection of the mode of operation takes place:

With the manual selector switch MSS in the position where the arm MAencounters the contact A, the clock timing mechanism is operative.Whenever the arm MAI encounters one of the segments 9, 12, 15, 18 acircuit is completed either through the up peak selector relay coil USRor thedown peak selector relay coil DSR (provided the coil BL is notenergised). If automatic selection of a peak has taken place immediatelyprior to completion of a circuit through the clock selector switch CSS,that peak condition remains set and is unaifected by the clockmechanism. When the clock time for a particular peak expires and thepeak traffic still persists, the peak selection is held by the automaticselection until the peak subsides.

When the manual selector switch MSS is moved so that the arm MAencounters the contact B, both automatic and clock selection areinoperative and the mode of operation remains normal irrespective ofchanges in the traffic conditions. When the arm MA is moved to encounterthe contact C or D, up peak and down peak respectively modes ofoperation are set and automatic selection and clock selection areinoperative. With the arm MA encountering the contact E, all selectionmechanism is inoperative.

I claim:

1. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy traffic in one directionand a second mode of operation that is suitable for normal trailicconditions, means associated with each car for determining whether thecar is loaded, and selection means for causing the cars to be operatedin the first mode when a predetermined time relationship exists betweenthe periods during which loaded cars are travelling in said onedirection and for causing the cars to be operated in said second modewhen no other mode is se lected.

2. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy trafic in one direction anda sec- 0nd mode of operation that is suitable for normal traflicconditions, means associated with each car for determining whether thecar is loaded, and selection means for causing the cars to be operatedin the first mode when a predetermined number of the cars travelling insaid one direction have been loaded with not more than a predeterminedtime interval between adjacent periods for which these cars are bothloaded and are travelling in said one direction, and for causing thecars to be operated in said second mode when no other mode is selected.

3. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy up traffic, a second modeof operation that is suitable for heavy down traflic and a third modethat is suitable for normal trafiic conditions, means associated witheach car for determining whether the car is loaded, and selection meansfor causing the cars to be operated in said first mode when apredetermined time relationship exists between the periods during whichloaded cars are travelling upwardly, for causing the cars to be operatedin the second mode when a second predetermined time relationship existsbetween the periods during which loaded cars are travelling downwardly,and for causing the cars to be operated in the third mode when no othermode is selected.

4. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy up traffic, a second modeof operation that is suitable for heavy down trafiic and a third modethat is suitable for normal traffic conditions, means associated witheach car for determining whether the car is loaded, and selection meansfor causing the cars to be operated in the first mode when apredetermined number of the cars travelling upwardly have been loadedwith not more than a predetermined time interval between adjacentperiods for which these cars are both loaded and travelling upwardly,for causing the cars to be operated in the second mode when apredetermined number of the cars travelling downwardly have been loadedwith not more than a predetermined time interval between adjacentperiods for which these cars are both loaded and travelling downwardly,and for causing the cars to be operated in the third mode when no othermode is selected.

5. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy up traffic, a second modeof operation that is suitable for heavy down traffic and a third mode ofoperation that is suitable when there is heavy traffic in neitherdirection, means for each car for determining whether the car is loaded,first means for each car for registering the loaded condition of the carwhen the latter is travelling upwardly, second means for each car forregistering the loaded condition of the car when the latter istravelling downwardly, and selection means for causing the cars to beoperated in the first mode when a first predetermined number of thefirst registering means have been operated for periods between adjacentones of which there is not more than a first predetermined time intervalduring which none of the first registering means is operated, forcausing the cars to be operated in the second mode when a secondpredetermined number of the second registering means have been operatedfor periods between adjacent ones of which there is not more than asecond predetermined time interval during which none of the secondregistering means is operated, and for causing the cars to be operatedin the third mode when no other mode is selected.

6. A control system as claimed in claim 5, wherein the first and secondintervals are of equal duration of time.

7. A control system as claimed in claim 5, wherein the first and secondpredetermined numbers of cars are each equal to the number of cars inthe system.

8. A control system for a plurality of cars arranged to serve a numberof floors, the system comprising means for operating the cars in any oneof a plurality of different modes, said modes including a first mode ofoperation that is suitable for heavy up traflic, a second mode ofoperation that is suitable for heavy down traffic and a third mode ofoperation that is suitable when there is heavy trafiic in neitherdirection, means foreach car for determining whether the car is loaded,first means for each car for registering the loaded condition of the carwhen the latter is travelling upwardly, second means for each car forregistering the loaded condition of the car when the latter istravelling downwardly, and selection means for causing the cars to beoperated in the first mode when a first predetermined number of thefirst registering means have been operated for periods between adjacentones of which there is not more than a first predetermined time intervalduring which none of the first registering means is operated, forcausing the cars to be operated in the second mode when a secondpredetermined number of the second registering means have been operatedfor periods between adjacent ones of which there is not more than asecond predetermined time interval during which none of the secondregistering means is operated, and for causing the cars to be operatedin the third mode when no other mode is selected, said selection meansincluding means for causing a mode other than the first mode to beselected when whilst the first mode is in operation said firstpredetermined interval occurs and means for causing a mode other thanthe second mode to be selected when whilst the second mode is inoperation said second predetermined interval occurs.

9. A control system for a plurality of cars arranged to serve a numberof fioors, the system comprising means for operating the cars in any oneof a plurality of ditferent modes, said modes including a first mode ofoperation that is suitable for heavy up trafiic, a second mode ofoperation that is suitable for heavy down traffic and a third mode ofoperation that is suitable when there is heavy traffic in neitherdirection, means for each car for determining whether the car is loaded,first means for each car for registering the loaded condition of the carwhen the latter is travelling upwardly, second means for each car forregistering the loaded condition of the car when the latter istravelling downwardly, selection means for causing the cars to beoperated in the first mode when a first predetermined number of thefirst registering means have been operated for periods between adjacentones of which there is not more than a first predetermined time intervalduring which none of the first registering means is operated, forcausing the cars to be operated in the second mode when a second predetermined number of the second registering means have been operated forperiods between adjacent ones of which there is not more than a secondpredetermined time interval during which none of the second registeringmeans is operated, and for causing the cars to be operated in the thirdmode when no other mode is selected, and means for preventing a changeof selection from the first mode to the second mode until after saidfirst predetermined interval has occurred and for preventing a change ofselection from the second mode to the first mode until after said secondpredetermined interval has occurred.

10. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavy up traffic, a second modeof operation that is suitable for heavy down trafiic and a third mode ofoperation that is suitable when there is heavy trafiic in neitherdirection, a load switch for each car for determining when theassociated car is loaded to a predetermined extent, first means for eachcar for registering the loaded condition of the car when the latter istravelling upwardly, second means for each car for registering theloaded condition of the car when the latter is travelling downwardly,and selection means for causing the cars to be operated in the firstmode when a first predetermined number of the first registering meanshave been operated for periods between adjacent ones of which there isnot more than a first predetermined time interval during which none ofthe first registering means is operated, for causing the cars to beoperated in the second mode when a second predetermined number of thesecond registering means have been operated for periods between adjacentones of which there is not more than a second predetermined timeinterval during which none of the second registering means is operated,and for causing the cars to be operated in the third mode when no othermode is selected.

11. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes, said modes including a firstmode of operation that is suitable for heavyup trafiic, a second mode ofoperation that is suitable for heavy down traific, a third mode ofoperation that is suitable when there is heavy traffic in neitherdirection and a fourth mode that is suitable for simultaneous heavy upand heavy down traflic, means for each car for determining whether thecar is loaded, first means for each car for registering the loadedcondition of the car when the latter is travelling upwardly, secondmeans for each car for registering the loaded condition of the car whenthe latter is travelling downwardly, and selection means for causing thecars to be operated in the first mode when a first predetermined numberof the first registering means have been opearted for the period betweenadjacent ones of which there is not more than a first predetermined timeinterval during which none of the first registering means is operated,for causing the cars to be operated in the second mode when a secondpredetermined number of the second registering means have been operatedfor periods between adjacent ones of which there is not more than asecond predetermined time interval during which none of the secondregistering means is operated, for causing the system to change from thefirst mode to the fourth mode when a third predetermined number of thesecond registering means have been operated for periods between adjacentones of which there is not more than a third predetermined time intervalduring which none of the second registering means is operated, forcausing the system to change from the second mode to the fourth modewhen a fourth predetermined number of the first registering means havebeen operated for periods between adjacent ones of which there is notmore than a fourth predetermined time interval during which none of thefirst registering means is operated, and for causing the cars to beoperated in the third mode when no other mode is selected.

12. A control system as claimed in claim 11, wherein the second andthird intervals are equal and the first and fourth intervals are equal.

13. A control system as claimed in claim 11, wherein the thirdpredetermined number is less than the second predetermined number andthe fourth predetermined number is less than the first predeterminednumber.

14. A control system as claimed in claim 11, wherein the selection meansincludes means for causing the system to change from the fourth mode toanother mode when any one of said intervals occurs.

15. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of diiferent modes of operation suitable fordifferent trafiic conditions, trafiic determining means for assessingtraffic in accordance with the'loading of the cars and the directions inwhich the cars are travelling, and selection mechanism for selecting themode in which the system operates in accordance with the traflic asassessed by said trafiic determining means.

16. A lift control system for a plurality of cars arranged to serve anumber of floors, the system comprising means for operating the cars inany one of a plurality of different modes of operation suitable fordifferent traffic conditions, traflic determining means for assessingtraific in accordance with the loading of the cars and the 12 directionsin which the cars are travelling, selection mechanism for selecting themode in which the system operates in accordance with the trafiic asassessed by said traffic determining means, and a manual selector switchfor setting the system to operate in a particular one of said modesirrespective of the loading of the cars and their directions of travel.

References Cited in the file of this patent UNITED STATES PATENTSThurston May 22, 1956

